The invention is directed to stacks of thin layers having thermal properties, especially solar-control or low-emissivity properties. The stacks being placed on transparent substrates in order to make windows for buildings and vehicles from them. The transparent substrates are organic substrates, of the polyacrylate or polymethyl methacrylate type or preferably, glass substrates. Preferably, the invention is directed to multilayer stacks capable of withstanding heat treatments at high temperatures of at least about 500xc2x0 C. to about 550xc2x0 C., which are used for treating glass for the purpose of bending, annealing and/or toughening it.
The stacks involved use silver-based functional layers surrounded by coatings made of dielectric material, especially for reducing light reflection, optionally having so-called xe2x80x9cblockerxe2x80x9d or xe2x80x9csacrificialxe2x80x9d metal layers between the functional layer and at least one of the coatings made of dielectric material.
Glazings provided with a low-emissivity multilayer stack make it possible to increase the thermal insulation. In the case of insulating glazing, it is possible, by the use of glass having an emissivity xcex5xe2x89xa60.1, on the face turned towards the intermediate gas layer, to substantially eliminate radiative exchange between the glass surfaces. Consequently, it becomes possible to manufacture insulating glazing having a K value of 1.1 W/m2K. Glazing having optimal low-emissivity multilayer stacks must, moreover, also have an overall energy transmission as high as possible, that is to say a g value as high as possible, in order to be able to use the solar energy within the energy budget. From the optical standpoint, the reflection color of the glazing must be relatively neutral, similar to that of conventional insulating glazing, and it is also attempted to obtain a light transmission as high as possible.
Multilayer stacks which at the very least partially fulfil these conditions have already been studied in various different forms and have, in principle, the general structure mentioned above.
Throughout this text, the term xe2x80x9ctransparent substratexe2x80x9d will generally be referred to as glass, but it being understood that this term may also encompass substrates made of plastics or other organic polymers. The substrate is only glass in the literal sense when it can withstand a heat treatment, such as bending or toughening at temperatures of about 550xc2x0 C. to about 650xc2x0 C.
It is becoming increasingly necessary to develop glazing products having low-emissivity multilayer stacks, which may be subjected to a prestressing heat treatment in order to increase the flexural strength of the glass and to give the glass safety properties. For this purpose, glass panes have to be heated to a temperature of more than 550xc2x0 C. to 650xc2x0 C., that is to say heated to their softening temperature, and then have to be suddenly cooled, when a toughening operation is involved. In this case, the layers are exposed to particularly high stresses which cannot always be withstood by the known low-emissivity stacks without deterioration. In the case of thermal stresses, layer modifications may in particular often occur which stem especially from oxidation and/or diffusion phenomena at the interface between the various layers.
Particular importance is attached, during a heat treatment of this kind, to the two sacrificial metal layers adjacent to the silver layer. Document DE 19,632,788 Al discloses a multilayer stack suitable for curved and/or prestressed (toughened) glass in which the sacrificial metal layers above and below the silver layer are composed each time of an AlMgMn alloy and have a thickness of 5 to 10 nm. At least one of the dielectric antireflection layers may be formed from several different oxides of the metals Sn, Zn, Ti, Si and Bi. In the case of this known multilayer system, the silver layer is admittedly protected against corrosion and deterioration by means of the two special layers of blockers at the high temperatures of the heat treatment, but it is not possible to achieve, however, in a satisfactory manner, simultaneously a very high light transmission, a very low emissivity and the desired color neutrality.
The present invention develops a multilayer stack which has a high overall light transmission, an extremely low emissivity and a neutral reflection color. This being so even after the stack has undergone a heat treatment at a moderate or a very high temperature, especially a treatment above about 550xc2x0 C. in order to curve, toughen or anneal the glass supporting the stack.
The present invention is directed to a transparent substrate comprising a multilayer stack comprising at least one silver-based functional layer between at least two layers of dielectric material with a metal layer provided between the silver-based functional layer and at least one of the dielectric material layers or coatings. The metal layer is an aluminum alloy of the formula AlM where M is at least one of the elements selected from the group consisting of Mg, Mn, Cu, Zn, Ni and Si. In one embodiment, the stacks can withstand a high-temperature heat treatment and have thermal properties, solar-control properties or low-emissivity properties.
In one particular embodiment, the stack comprises the layer sequence:
D1/ZnO/Ag/AlM/D2/ZnMxe2x80x2O
wherein Ag denotes the silver-based functional layer, AlM is an aluminum alloy containing at least one of the elements selected from the group consisting of Mg, Mn, Cu, Zn, Ni and Si; ZnMxe2x80x2O is a mixed oxide of zinc and at least one other metal designated at Mxe2x80x2, and the ZnMxe2x80x2O has a spinel structure; D1, D2 or both are a layer or a superposition of layers comprising at least one layer made of a metal oxide selected from the group consisting of SnO2, Bi2O3, TiO2, ZnO, silicon nitride, a metal nitride, a mixed silicon/metal nitride and mixtures thereof. The mixed silicon/metal nitride can be selected from the group consisting of Si3N4, AlN, SiAlN, SiZrN and mixtures thereof.
D1, D2, or both can be a superposition of three layers having a low refractive index of less than 1.75. D1, D2, or both are made of SiO2 optionally containing A12O3, flanked by two layers having a refractive index greater than 1.9 and made of compounds selected from the group consisting of SnO2, Bi2O3, TiO2, ZnO, Si3N4, AlN, SiAlN, SiZrN and mixtures thereof.
The aluminum alloy AlM may comprise from about 45% to about 99% by weight of aluminum and from about 55% to about 1% by weight of one or more other metals. Preferably, the aluminum alloy AIM comprises more than about 80% aluminum, from about 2% to about 8% zinc and from 0% to about 3% magnesium.
In another embodiment of the invention, the stacks may further comprise a metal layer inserted between the ZnO layer and the silver layer wherein the metal is Zn.
The mixed zinc oxide ZnMxe2x80x2O is obtained by reactive sputtering using a target made of a metal alloy containing Zn, Sn and Al, Sb, or a mixture thereof. Preferably, the mixed zinc oxide ZnMxe2x80x2O is obtained by reactive sputtering using a target made of a metal alloy containing Zn present in an amount of about 60% to about 80%, Sn present in an amount of about 20% to about 40% and Al or Sb present in an amount of about 1% to 5% by weight of the alloy. Preferably, the metal alloy comprises about 68% Zn, about 30% Sn and about 2% Al or Sb by weight.
The invention also comprises a monolithic, laminated or multiple glazing comprising a transparent glazing sheet that includes on one surface the transparent substrate described herein. Preferably, the glazing sheet is glass or plastic.
The invention is directed to a transparent substrate, especially a glass substrate, provided with a multilayer stack having thermal properties, especially solar-control or low-emissivity properties, which is especially capable of undergoing the above-mentioned heat treatments and which comprises at least one silver-based functional layer surrounded by two coatings made of dielectric material, with the presence of metal layers, preferably thin layers, between the functional layer and at least one of the two coatings. The stack of the invention is characterized by the following sequence:
D1/ZnO/Ag/AlM/D2/ZnMxe2x80x2O
wherein AlM is an aluminum alloy containing at least one of the following elements: Mg, Mn, Cu, Zn, Ni, Si; ZnMxe2x80x2O is a mixed oxide of zinc and at least one other metal, preferably having a spinel structure; D1, D2 or both are either a layer or a superposition of layers comprising at least one layer made of a metal oxide such as SnO2, Bi2O3, TiO2, ZnO or made of silicon nitride or of a metal nitride such as Si3N4 or AlN or made of a mixed silicon/metal nitride, such as SiAlN or SiZrN.
The formulae AlM, ZnMxe2x80x2O, SiAlN and SiZrN make no assumptions about the stoichiometry of each of the elements and have been adopted for the sake of simplifying the text. It goes without saying that AlzMy, ZnxMxe2x80x2yOz, etc., are also included where x, y, z, are integers.
xe2x80x9cThin layersxe2x80x9d as used herein, unless otherwise define should be understood to mean layers deposited in essentially metallic form and with a thickness substantially less than that of the silver layer, of the order of about 0.5 nm to about 5 nm, which layers are capable of being partially oxidized/modified during the deposition or during a heat treatment after the deposition. These layers are often referred to by the term xe2x80x9csacrificialxe2x80x9d layers when above the silver or xe2x80x9cblockerxe2x80x9d layers, when above and/or below the silver.
Advantageously, D1 and/or D2 are single, double or triple layers. This may be, in a preferred embodiment, a superposition of three layers, including at least one layer having a low index of refraction of less than about 1.75 and preferably, less than about 1.65, such as about 1.45 to about 1.63. The central layer can be made of SiO2and/or AlzOY and flanked by two layers of higher refractive index, for example greater than about 1.9, preferably about 2 to about 2.5 and made of materials mentioned above such as: Bi2O3, SnO2, TiO2, ZnO, Si3N4, AlN, SiAlN and SiZrN.
Preferably, the aluminum alloy AlM comprises from about 45% to about 99% by weight of Al and from about 55% to about 1% by weight of one or more other metals or similar materials, such as silicon. It may especially be an alloy containing by weight at least about 80% Al, preferably from about 90% to about 98% Al, from about 15 2% to about 3% Zn and from 0% to about 3% Mg. An example is an alloy comprising approximately 94% Al, 5% Zn and 1% Mg by weight.
Preferably, a metal layer is inserted between the ZnO layer beneath the silver layer and the silver layer. It is preferably made of Zn. It may also be made of other metals, such as Sn, Ti and NiCr.
Preferably, the mixed zinc oxide ZnMxe2x80x2O is obtained by reactive sputtering using a target made of a metal alloy containing Zn, Sn and Al and/or Sb, especially in the following proportions by weight: Zn present in an amount of about 60% to about 80%, preferably about 68%; Sn present in an amount of about 20% to about 40%, preferably about 30%; and Al or Sb present in an amount of about 1% to about 5%, preferably about 2%.
In general, it may be considered that these proportions are more or less maintained in the mixed oxide layer thus obtained. It is preferable for the Zn proportion with respect to the other metals in the layer to be at least about 50% and preferably at most about 75% to about 80%, thereby allowing a spinel structure to be produced. With too high an amount of zinc, there is a risk of forming ZnO particles and of affecting the chemical durability of the layer. The third element Al or Sb allows the ZnO particles to be xe2x80x9cdopedxe2x80x9d and thus to make them more moisture resistant. The fact is that the layer of the invention is particularly hard and thus serves as a hard overlayer for protecting the rest of the stack.
The following are three non-limiting embodiments of stacks, preferably on glass:
(a) SnO2/ZnO/Zn/Ag/AlZnMg/SnO2/ZnSnAlO;
(b) SnO2/ZnO/Zn/Ag/AlZnMg/SnO2/SiO2/SnO2/ZnSnAlO; and
(c) SnO2/ZnO/Zn/Ag/AlZnMg/SnO2/A12O3/SnO2/ZnSnAlO;
wherein AlZnMg and ZnSnAlO are made without any assumptions about the relative proportions between the various elements of each of the two types of layers. It should be noted that it is possible to replace Al with Sb in the layer of mixed zinc oxide.
A subject of the invention is also the monolithic, single rigid substrate, laminated or multiple glazing incorporating the coated substrate described above.
Another preferred embodiment of the present invention relates to a multilayer stack having the following structure of layers: glass xe2x80x94MOxe2x80x94ZnOxe2x80x94Znxe2x80x94Agxe2x80x94AlMxe2x80x94MOxe2x80x94ZnMO, wherein MO is a metal oxide such as SnO2, Bi2O3, TiO2 or ZnO, AlM is an aluminum alloy containing one or more of the elements Mg, Mn, Cu, Zn and Si as the alloying constituent, and is ZnMO being a composite oxide, containing ZnO, of the spinel type.
In these preferred embodiments, it is only by virtue of the interaction of the various layers, namely the Zn metal layer, which is optional, as the lower sacrificial metal layer, the Al alloy as the upper sacrificial metal layer and an upper antireflection layer with a partial layer made of a mixed oxide, advantageously containing ZnO and having a spinel structure, that a multilayer stack capable of undergoing bending or toughening is produced, which stack fulfils all the requirements with regard to extremely low emissivity, light transmission and color neutrality in reflection and which can, in addition, be manufactured in industrial deposition plants without any technical problem and in an economic manner.
DE 19,607,611 Cl discloses multilayer stacks in which the dielectric antireflection layers are composed of ZnO may be subjected to high thermal stresses and are suitable for prestressing the glass. Sputtering ZnO often causes a problem during practical operation in the sputtering chamber: more deposits are formed than for other metal oxides, which deposits disturb the sputtering process and result in defective layers. This drawback is minimized in the case of the multilayer stack according to the invention because of the fact that, in order to form the antireflection layers, ZnO is used to a lesser extent for forming the partial layer, while the other partial layers are formed from other oxides, such as SnO2 for example, which exhibit much better behavior during the sputtering process. The term xe2x80x9cpartialxe2x80x9d as used herein, unless otherwise indicated, means that ZnO does not constitute the entire thickness of the dielectric coatings on either side of the silver layer.
For the aluminum alloy forming the upper sacrificial metal layer, alloys having an Al content from about 45% to about 99% by weight are preferably used.
A preferred composition of the spinel-type mixed zinc oxide according to the invention comprises from about 35% to about 70% by weight of Zn, from about 29% to about 64.5% by weight of Sn and from about 0.5% to about 6.5% by weight of at least one of the following elements: Al, Ga, In, B, Y, La, Ge, Si, P, As, Sb, Bi, Ce, Ti, Zr, Nb and Ta.